Vancouver draws its drinking water from reservoirs in the Capilano, Seymour, and Coquitlam watersheds. Pipelines distribute these waters throughout the Vancouver area. Landslides in the watersheds are natural phenomena that usually occur during heavy rains, exposing soil to erosion. This allows mud to wash into reservoirs where it enters the water system. While cloudy water is not itself a health risk, silt and clay can reduce the ability of chlorine to kill bacteria and other microorganisms. Natural phenomena, such as wildfires, or poor forestry practices can also increase the incidence of landslides within B.C.'s mountainous areas.
Vancouver's watersheds have naturally acidic waters which tend to corrode pipes, dissolving copper, iron, zinc, and lead. Elevated levels of lead in drinking waters can pose a health concern. The waters are acidic because the area is underlain by rocks resistant to chemical reactions that reduce the natural acidity of rain. Also, rainwater rapidly runs off the steep slopes, leaving little time for these chemical reactions. Plans are in place to reduce this water acidity through improvements in the water treatment process.